We propose to develop new monomer formulations for use in dental applications which would undergo expansion on polymerization. These should produce polymer materials particularly suited for high strength, stress-free composites, pit and fissure sealants with superior adhesion, accurate die materials and precision denture resins. Specifically, we propose synthesis of spiro othocarbonate monomers capable of free radical polymerization. Analogues of these proposed monomers have previously been synthesized in these laboratories and shown to exhibit polymerization expansion. The proposed monomers will be tested in various comonomers formulatons with currently available dental composite, pit and fissure sealants and denture resins such that polymerization with near zero shrinkage or controlled expansion will occur. The effect of these monomers on the physical characteristics of strength, hardness, adhesion, absorption, solubility, color stability and toxicity of the dental resin will be determined. These results will be used to guide the synthesis of modified spiro orthocarbonates to give comonomer systems with the required polymerization expansion, reactivity, physical and toxicological properties. The objectives of the study are to: (1) Synthesize spiro orthocarbonate monomer derivatives capable of free radical polymerization. (2) Determine the reactivity and the degree of polymerization expansion of these monomers. (3) Determine the ability of these monomers to copolymerize with various dimethacrylate adducts and the volume ratios required for zero or positive volume changes on polymerization. (4) Determine the suitability of these comonomer formulations for dental use based upon physical properties and toxicity.